The long-range objective of this research is to investigate the physiological mechanisms of liquid ventilation with the aim of developing a therapeutic method for treating newborn infants with severe respiratory distress, such as those with hyaline membrane disease and severe meconium aspiration syndrome. The proposed research can be grouped as follows: 1. To determine in vivo pressure gradients along the trachea during liquid ventilation and the distribution of viscous and inertial losses. These studies will correlate dynamic intratracheal pressure with airway deformation and provide guidelines for optimum modes of liquid ventilation (frequency, tidal volume, flow). 2. To investigate the changes in cardiovascular dynamics during ventilation with oxygenated liquid, and the effects of compensatory cardiovascular adjustments on acid-base homeostasis. These studies will include the relative influence of liquid lung volume, tidal volume, and breathing frequency on cardiovascular function, and suggest liquid ventilatory patterns for effective gas exchange at the level of the tissues. 3. To evaluate the clinical and physiological significance of liquid ventilation and lung lavage for alveolar debridgement using animal models. Gaseous exchange, acid-base status, and pulmonary mechanics measurements will be determined before and after liquid ventilation or lavage. These results will: a) quantify the relationship between duration of therapy (brief lavage vs. hours of liquid ventilation) and subsequent alterations in gas exchange and mechanical behavior of the lung, and b) elucidate the effectiveness of liquid ventilation as an intermediate term (several hours) respiratory support modality for severe aspiration syndromes.